package org.light.framework.util;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * id生成器
 * @author Administrator
 *
 */
public class IdGenerator {
	
	private long workerId;
	private long datacenterId;
	private long sequence = 0L;
	private long twepoch = 1288834974657L; // Thu, 04 Nov 2010 01:42:54 GMT
	private long workerIdBits = 5L; // 节点ID长度
	private long datacenterIdBits = 5L; // 数据中心ID长度
	private long maxWorkerId = -1L ^ (-1L << workerIdBits); // 最大支持机器节点数0~31，一共32个
	private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 最大支持数据中心节点数0~31，一共32个
	private long sequenceBits = 12L; // 序列号12位
	private long workerIdShift = sequenceBits; // 机器节点左移12位
	private long datacenterIdShift = sequenceBits + workerIdBits; // 数据中心节点左移17位
	private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits; // 时间毫秒数左移22位
	private long sequenceMask = -1L ^ (-1L << sequenceBits); // 4095
	private long lastTimestamp = -1L;

	public static IdGenerator get() {
		return IdGenHolder.instance;
	}

	public IdGenerator() {
		this(0L, 0L);
	}

	public IdGenerator(long workerId, long datacenterId) {
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}

	public synchronized long nextId() {
		long timestamp = timeGen(); // 获取当前毫秒数
		// 如果服务器时间有问题(时钟后退) 报错。
		if (timestamp < lastTimestamp) {
			throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
		}
		// 如果上次生成时间和当前时间相同,在同一毫秒内
		if (lastTimestamp == timestamp) {
			// sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
			sequence = (sequence + 1) & sequenceMask;
			// 判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp); // 自旋等待到下一毫秒
			}
		} else {
			sequence = 0L; // 如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
		}
		lastTimestamp = timestamp;
		// 最后按照规则拼出ID。
		// 000000000000000000000000000000000000000000 00000 00000 000000000000
		// time datacenterId workerId sequence
		return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
	}

	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	protected long timeGen() {
		return System.currentTimeMillis();
	}

	private static class IdGenHolder {
		private static final IdGenerator instance = new IdGenerator();
	}

	public static void main(String[] args) {
		long avg = 0;
		for (int k = 0; k < 10; k++) {
			List<Callable<Long>> partitions = new ArrayList<Callable<Long>>();
			final IdGenerator idGen = IdGenerator.get();
			for (int i = 0; i < 1400000; i++) {
				partitions.add(new Callable<Long>() {
					@Override
					public Long call() throws Exception {
						long a = idGen.nextId();
						System.out.println(a);
						return a;
					}
				});
			}
			ExecutorService executorPool = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
			try {
				long s = System.currentTimeMillis();
				executorPool.invokeAll(partitions, 10000, TimeUnit.SECONDS);
				long s_avg = System.currentTimeMillis() - s;
				avg += s_avg;
				System.out.println("完成时间需要: " + s_avg / 1.0e3 + "秒");
				executorPool.shutdown();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		System.out.println("平均完成时间需要: " + avg / 10 / 1.0e3 + "秒");
	}
}
